Concern has been growing in recent times over energy consumption in the United States and abroad. The cost of energy has steadily risen as power utilities try to cope with continually growing demand, increasing fuel prices, and stricter regulatory mandates. Power utilities must also maintain existing infrastructure, while simultaneously finding ways to add more generation capacity to meet future needs, both of which add to the cost of energy. Moreover, burgeoning energy consumption continues to impact the environment and deplete natural resources.
A major portion of the rising cost of energy is borne by consumers, who, despite the need, remain poorly-equipped to identify the most cost effective ways to lower their energy consumption. No-cost behavioral changes, such as adjusting thermostat settings and turning off unused appliances, and low-cost physical improvements, such as switching to energy-efficient light bulbs, may be insufficient to offset increases in monthly utility bills, particularly as seasonal space heating and air conditioning (AC) together consume the most energy in the average home. As a result, appreciable decreases in energy consumption can usually only be achieved by investing in upgrades to a building's heating or cooling envelope or “shell.” However, identifying and comparing those improvements to a building's shell that will yield an acceptable return on investment in terms of costs versus energy savings requires determining building-specific parameters, especially the building's thermal conductivity (UATotal).
Heating, ventilating, and air conditioning (HVAC) energy costs are tied to a building's thermal conductivity UATotal. A poorly insulated home or a building with significant sealing problems will require more HVAC usage to maintain a desired interior temperature than would a comparably-sized but well-insulated and sealed structure. Reducing HVAC energy costs is not as simple as choosing a thermostat setting that causes an HVAC system to run for less time or less often. Rather, HVAC system efficiency, duration of heating or cooling seasons, differences between indoor and outdoor temperatures, and other factors combined with thermal conductivity UATotal can weigh into overall energy consumption.
Conventionally, an on-site energy audit is performed to determine a building's thermal conductivity UATotal. A typical energy audit involves measuring the dimensions of walls, windows, doors, and other physical characteristics;
approximating R-values of insulation for thermal resistance; estimating infiltration using a blower door test; and detecting air leakage using a thermal camera, after which a numerical model is run to solve for thermal conductivity. The UATotal result is combined with the duration of the heating or cooling season, as applicable, over the period of inquiry and adjusted for HVAC system efficiency, plus any solar (or other non-utility supplied) power savings fraction. The audit report is often presented in the form of a checklist of corrective measures that may be taken to improve the building's shell and HVAC system, and thereby lower overall energy consumption. As an involved process, an energy audit can be costly, time-consuming, and invasive for building owners and occupants. Further, as a numerical result derived from a theoretical model, an energy audit carries an inherent potential for inaccuracy strongly influenced by physical mismeasurements, lack of measurements, data assumptions, and so forth. As well, the degree of improvement and savings attributable to various possible improvements is not necessarily quantified due to the wide range of variables.
Therefore, a need remains for a practical model for determining actual and potential energy consumption for the heating and cooling of a building.
A further need remains for an approach to quantifying improvements in energy consumption and cost savings resulting from building shell upgrades.